Wells having a production string of tubing that includes vertically spaced side pocket mandrels arranged for placing, retrieving and manipulating flow control devices such as gas lift valves, are used extensively in gas and oil well production operations. Each of the mandrels generally includes an open-topped side pocket that is laterally offset to the side of the mandrel bore. A placement and removal tool known as a "kick-over" tool is lowered through the tubing to the level of the mandrel to effect placement or removal of a valve assembly in the side pocket. As mentioned, the device can be a gas lift valve that includes a dome pressure operated regulator valve, and which is held in the pocket by a latch assembly that engages a shoulder above the top of the pocket.
Prior side pocket mandrels generally have been constructed with a main bore that is aligned with the bore of the well tubing and a side pocket that is laterally offset from the main bore. Examples of such devices are shown in U.S. Pat. Nos. 2,824,525, 3,268,006, and 3,741,299. The main bore of the mandrel allows various wire line tools to pass therethrough for the performance of well operations below the mandrel while a flow control device is positioned in the side pocket. The side pocket typically has polish bores at the upper and lower ends thereof that are engaged by spaced packing rings in the flow control device, and a plurality of ports through the wall thereof to communicate gas from the well annulus to a valve element that controls the injection of the gas into the tubing string. In many instances in the prior art, the mandrel assembly is made as a weldment of swedge nipples to the ends of a round or oval pipe section, which is a construction that is inherently weak and subject to corrosion at the weld points. Moreover, a weldment is more difficult to protect through use of an internal plastic coating.
Prior art mandrels also have been provided with deflector means for protecting flow control devices positioned in the side pocket, and guide means for preventing tools moving through the well tubing from catching and hanging in the mandrel. Examples of such devices are disclosed in U.S. Pat. Nos. 3,741,299, 3,802,503, 4,106,503, and 4,106,564.
The side pocket of the typical prior art mandrel generally is enclosed within the mandrel body, and thus the condition of the bore of the side pocket cannot be observed prior to running. A worn-out or corroded bore in the side pocket may result in having to pull the entire string of well tubing--a very costly and time-consuming operation. Furthermore, the machining of these mandrels has not allowed for precision work in connection with the maintenance of close tolerances, or visual inspection which invariably results in excessive manufacturing costs.
Additionally, in mandrels having an internal side pocket, the flow control devices that are seated therein are in contact with noxious well fluids and subject to varying temperatures which require that the devices be designed to meet these conditions. This results in the use of expensive materials for construction of the flow control devices and the performance of tedious calculations for temperature corrections.
It is a common occurrence for the flow control devices to be difficult or even impossible to remove. The usual flow control device seats within a side pocket that is aligned parallel to the longitudinal axis of the main bore of the mandrel. As mentioned above, two sets of packing are used to seal the flow control device within the pocket, one near the top of the device and one near the bottom. Due to the parallel alignment of the flow control device relative to the main bore, and to the use of the two sets of packing, a removal tool has to make a long straight pull on the flow control device upwardly through the side pocket in order to remove the device from its seat. The conventional removal tools inherently pull on the valve latch at an angle which places the latch and the flow control device in a bind, thereby causing, in many instances, bent or broken flow control devices and latches. Such damage may result in a costly pulling job, and oftentimes may require the replacement of equipment.
The presence of two sets of packing may also cause a great amount of friction when removing the valve from the side pocket seats. This is due to the fact that the annular area between the device and the pocket wall above the lower packing element can become filled with sand and debris through which the packing must be pulled in order to remove the device from the side pocket. This increase in pulling force, and the inclination thereof with respect to vertical as discussed above, provides a further basis for damaging the rather slender and delicate valves and latches when removal becomes necessary.
It has been typical practice to machine the polish bores that are engaged by the two sets of packing on the flow control device on the same diameter so that the device is balanced with respect to fluid pressures. However, with a balanced design, the operator cannot determine if the flow control device is properly set in the first instance. If the flow control device is not properly set, it may hold in one direction and not the other, and this condition may not become apparent until the wire line crew has left the well site and the proper equipment to correct the situation have been moved off location.
A further disadvantage of prior structures is that the side pocket mandrels have required that retrievable-type flow control devices be utilized, negating the use of conventional type flow control devices within this type of equipment.
The kickover tools of the prior art are generally activated by pulling dogs on the tool up against a shoulder in the mandrel to release the kickover arm that caries the flow control device. The arm is biased outwardly so that its outward movement aligns the bottom nose of the device with the side pocket of the mandrel. Downward movement and jarring are then used to insert the flow control device into the side pocket and to release the arm from the latch which engages underneath a shoulder to hold the device in the pocket. Since the kickover arm and flow control device are normally biased outwardly, there is always a considerable risk of the tool being prematurely activated which can cause it to drag and hang up in the tubing. Some of the latches included in the valve assemblies of the prior art are drilled through to permit the gas from the flow control device to enter into the main bore of the mandrel. Such construction limits the available gas flow area.
The general object of the present invention is to provide a new and improved side pocket mandrel, kickover tool, and combination of elements that alleviates most, if not all, of the foregoing disadvantages.